Re: [PATCH v2] builtin/blame: fix out-of-bounds read with excessive `--abbrev`

> Hi Jialuo,
> 
> On Thu, 9 Jan 2025, shejialuo wrote:
> 
> > On Thu, Jan 09, 2025 at 12:48:22PM +0100, Patrick Steinhardt wrote:
> >
> > > +		printf("%.*s", (int)length, hex);
> > >  		if (opt & OUTPUT_ANNOTATE_COMPAT) {
> > >  			const char *name;
> > >  			if (opt & OUTPUT_SHOW_EMAIL)
> > > diff --git a/t/t8002-blame.sh b/t/t8002-blame.sh
> > > index 0147de304b4d104cc7f05ea1f8d68f1a07ceb80d..7cf6e0253a5bbd4d6e438e627dc18b47eac4df66 100755
> > > --- a/t/t8002-blame.sh
> > > +++ b/t/t8002-blame.sh
> > > @@ -126,6 +126,10 @@ test_expect_success '--no-abbrev works like --abbrev with full length' '
> > >  	check_abbrev $hexsz --no-abbrev
> > >  '
> > >
> > > +test_expect_success 'blame --abbrev gets truncated' '
> > > +	check_abbrev $hexsz --abbrev=9000 HEAD
> > > +'
> > > +
> >
> > By the way, I feel this usage is a little strange as the user side. When
> > I received the report mail from Johannes today morning, I feel a little
> > funny that we allow the value of the `--abrrev` option exceeds the
> > `GIT_MAX_HEXSZ` in the first place.
> 
> See the explanation I provided in
> https://lore.kernel.org/git/c439fcaf-11af-7862-9c3c-18dc0842b57d@gmx.de/:
> When calling `git blame --abbrev=40 HEAD.. -- <file>` (in a SHA-1-based
> repository), the OIDs are prefixed with a `^` and then the last hex digit
> will be cut. The reason? Git wants to align the text after the OID.
>